In a typical method for measuring a blood glucose level, redox reaction is utilized. Meanwhile, portable handheld blood glucose level measuring apparatuses are widely used so that the blood glucose level can be measured easily at home or away from home. In such a portable blood glucose level measuring apparatus, the blood glucose level is measured by mounting a disposable biosensor for providing an enzymatic reaction field to the apparatus and supplying blood to the biosensor.
The measurement of a blood glucose level may be performed by utilizing an electrochemical technique. In such a case, the blood glucose level is measured by mounting a biosensor 90 to a blood glucose level measuring apparatus 91 in such a manner as shown in FIG. 14 (See JP-B-H8-10208, for example). The biosensor 90 includes an insulating substrate 92 formed with a first and a second electrodes 93 and 94 for applying voltage to the enzymatic reaction field. The blood glucose level measuring apparatus 91 comprises a connector 97 including a first and a second terminals 95 and 96 coming into contact with the first and the second electrodes 93 and 94, and a measurement circuit 98 for determining the blood glucose level based on the information from the connector 97.
The blood glucose level measuring apparatus is affected by various disturbing noise. The disturbing noise may influence the measurement result or destroy the electronic part to make the measurement impossible. Particularly, a portable small measurement apparatus is liable to be influenced by static electricity from a human body. Specifically, since the biosensor 90 is usually mounted to the blood glucose level measuring apparatus 91 manually, the static electricity, if built up in the human body, is discharged to the first and the second electrodes 93 and 94 of the biosensor 90 or the first and the second terminals 95 and 96 of the blood glucose level measuring apparatus 91. If no countermeasure is taken against the static electricity, the static electricity is inputted, as disturbing noise, into the measurement circuit 98 through the first electrode 93 and the first terminal 95, for example. Therefore, as the conventional measures to reduce the influence of static electricity, the arrangement of the first and the second terminals 95 and 96 in the blood glucose level measuring apparatus 91 has been contrived or the withstand voltage of each electronic part constituting the measurement circuit 98 has been increased. In another method to cope with static electricity, a conductive sheet is disposed adjacent to the connector or the nearby portion (See JP-Y-H8-2609, for example).
However, the above-described conventional countermeasures against disturbing noise are realized by modifying the design of the blood glucose level measuring apparatus 91. Therefore, such countermeasures complicate the structure of the blood glucose level measuring apparatus 91 and increase the size of the apparatus, and hence, increase the manufacturing cost.
Recently, there is a tendency to reduce the thickness of the first and the second electrodes 93 and 94 to reduce the manufacturing cost of the biosensor 90. Further, to adapt the biosensor 90 to the portable blood glucose level measuring apparatus 91, the size of the biosensor 90, including the size of the first and the second electrodes 93 and 94, cannot help being reduced. In such cases, the resistance of the first and the second electrodes 93 and 94 increases. Therefore, in the circuit structure shown in FIG. 14, for example, Joule heat is generated adjacent to the contact point between the first electrode 93 and the first terminal 95 of the blood glucose level measuring apparatus 91 when static electricity tries to move through the contact point. When the generated Joule heat is high, the first electrode 93 may melt. In such a case, the biosensor 90 mounted to the apparatus cannot measure the blood glucose level. Further, the melt of the first electrode 93 of the biosensor 90 adheres to the first terminal 95 of the blood glucose level measuring apparatus 91 and changes the resistance of the first terminal 95, so that an error is generated in the subsequent measurement of responsive current. Such a problem is more significant as the thickness of the first electrode 93 is made smaller.